(1) Field of the Invention
This invention relates to a drive device for coolant pumps in liquid-cooled internal combustion engines.
(2) Description of the Prior Art
In internal combustion engines of the liquid cooled type for tractors and agricultural machines in particular, a coolant pump, which is normally installed in the cover of the crankcase or transmission case, is driven by a crankshaft or camshaft through a train of gears to move coolant by the rotation of an impeller to be circulated through a coolant jacket for engine cooling during the operation. The impellers of such pumps are mounted on a rotatably disposed shaft which is driven by a driven gear secured to the shaft, with the gear in turn being driven by a driven gear mounted on the crankshaft or camshaft.
In the prior art coolant pumps, referring to FIGS. 5 and 6 illustrating the two typical conventional coolant pumps, a pump 7 comprises a pump shaft 11 carrying at a rear end thereof an impeller 10 and a pump body 8 including an inlet port 35 to admit the coolant into the pump body 8. The rotation of the impeller 10 causes the coolant to move, by the action of centrifugal force, into an outlet and circulate through a coolant jacket 38 cooling the engine 1.
A driven gear 15 is secured to a front end portion of the pump shaft 11 and is connected in mesh engagement with a crankshaft gear 17 through an intermediate gear such as a camshaft gear 16 which drives the pump shaft 11 and hence the impeller 10 through the driven gear 15 when the engine 1 is running. The pump body 8 includes a boss 8a with a central bore in which the pump shaft 11 is supported adjacent to its front end through bearings 40, which may be provided in a pair in the boss bore, as may best be depicted in FIG. 6. Also, the pump 7 comprises an annular mechanical seal 30 and a sealing ring 34 mounted about the shaft 11 adjacent to the impeller 10 to prevent leakage of coolant from the pump body 8 down along the circumference of the pump shaft 11.
The pump shaft 11 is pressure fitted into the central bore of the driven gear 15, with such force as to prevent the driven gear 15 to slip around the pump shaft circumference during the operation, since the pump shaft is under increased thrust load exerted on its periphery by the mechanical seal 30 in a way to counteract the pump shaft rotation. In some instances where pumps employ a driven gear 15 made of synthetic resin material, in order to insure proper transmission of the torque from the driven gear 15 to the pump shaft 11, a bushing 13 made of metal material is formed in the central bore of the driven gear 15 into which the pump shaft 11 is pressure inserted, as may best depicted, .in FIG. 5. As shown, the bushing 13 may be made to contact the front face 8b of the boss 8a so as to prevent the pump shaft 11 from coming off from its bore in the pump body 8.
However, these conventional coolant pumps have been known to pose various problems owing to their designs. First, the use of two ball bearings 40 in the boss 8a add extra parts and assembling costs and weight. Furthermore, this arrangement require a rather great length of shaft on the impeller side. Another problem is that the use of a metal bushing 13 made integrated with the driven gear 15 complicates the construction, with a resultant increase in production costs.
The present invention has been proposed to eliminate the above-mentioned disadvantages with the prior art coolant pumps.